Charger connected to a load via a switching circuit to prevent an incorrect polarity connection

ABSTRACT

The invention relates to an electronic circuit for a power supply device ( 1 ), in particular for a charger ( 2 ) for accumulators ( 3 ), in which the power supply device ( 1 ) is connected via input terminals ( 4, 5 ) to a power source ( 6 ), the power supply device ( 1 ) converting the supplied power from any voltage, in particular an AC voltage, into a DC voltage and this transformed power is forwarded via output terminals ( 7, 8 ) to a consumer ( 9 ), in particular the accumulator ( 3 ), in which, a switching element ( 10 ) is provided as a means of operating polarity reversal protection. The switching element ( 10 ) is disposed between at least one output terminal ( 7, 8 ) and a potential, in particular a negative potential, of the power supply device ( 1 ) and if a specific polarity appears at this output terminal ( 7, 8 ) the switching element ( 10 ) is connected through and if an opposite (incorrect) polarity appears it is switched off. The output terminals ( 7, 8 ) are disconnected separated from the input terminals ( 4, 5 ), in particular from the power source ( 6 ), by the power supply device ( 1 ).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of AUSTRIAN ApplicationNo. A 1111/2000 filed on Jun. 28, 2000. Applicants also claim priorityunder 35 U.S.C. §365 of PCT/AT01/00193 filed on Jun. 12, 2001. Theinternational application under PCT article 21(2) was not published inEnglish.

The invention relates to a charger device connected to an accumulatorand combined with a protection circuit for reverse polarity and overloadprotection, and a method of controlling the power supply device.

Patent specification DE 197 56 825 A1 describes a polarity reversalprotection circuit with a switching element disposed between an inputterminal and an output terminal, which does not allow a current flowunless the voltage at the input terminal is of a certain polarity. If aspecific polarity is applied to the input terminal, the switchingelement connects through and if the polarity is not correct, it isopened or deactivated. The disadvantage of this system is that there isprotection on the input side only.

An electronic circuit with polarity reversal protection is also knownfrom patent specification DE 197 17 527 A1, in which a switchingelement, in particular a MOS field-effect transistor, is connectedbetween an input source connected to a DC voltage source and adownstream circuit structure, and the switching element is activated ifthe DC voltage source is at the correct polarity and deactivated if thepolarity is not correct. Again, the disadvantage of this approach isthat there is protection on the input side only.

Patent specification DE 40 31 228 C1 discloses a circuit designed toprotected against incorrect polarity, in which a field-effect transistor(FET) is disposed between a DC voltage supply source (Q) and a consumer(V) in the positive or negative line. The gate terminal of thefield-effect transistor is always connected via a diode (D1) to theantipole or the line in which the field-effect transistor is notdisposed. If a situation arises in which the polarity is not correct, aclearing current (IA) flows across the diode (D1), as a result of whichthe gate capacitance is discharged at the FET and the field-effecttransistor is switched off with virtually no delay. Once the DC voltagesource is correctly polarized again, the field-effect transistor ischarged with the gate source capacitance again because the diode DI isnow in the locked position so that the gate capacitance of the FET canbe re-charged and the consumer current IV is able to flow across itagain. The disadvantage of this solution is that the circuit design canbe used to protect against incorrect polarity only and can not be usedto provide other safety features.

The object of the invention is to provide a charger connected to anaccumulator and a method of controlling the power supply, which willprotect the power supply on the output side, such as a polarity reversalprotection, an overload protection and/or a load detection system.

This object is achieved by the invention due to the fact that a controlmode of a first switching element in the protection circuit is connectedto another switching element to which a negative potential of thecharger device can be switched, or to a control output of a controldevice of the charger device, and the control mode is also connected toa positive potential of a supply voltage source. The switched state ofthe first switching element is determined by the switched state of theother switching element. The advantage of this approach is that acircuit design of this type does not require a counter voltage to chargean accumulator, which enables fully discharged accumulators to becharged. Another advantage resides in the fact that not only can acharger device of this type be used to charge accumulators, it can alsobe used to supply energy for another consumer because other safetyfeatures can be run in addition to polarity reversal protection, such asoverload protection and a load detection system, for example.

The object is also achieved by a method in which, when the chargerdevice is connected to the power source, the first switching element forthe polarity reversal protection is activated, even if the accumulatoris not connected, and if the opposite (incorrect) polarity appears atthe output terminals, another switching element is activated, as aresult of which the voltage applied to a control node of the firstswitching element is applied to the negative potential, therebyswitching off or deactivating the first switching element.

The invention will be explained in more detail with reference topresently preferred embodiments.

In the drawings:

FIG. 1 is a simplified circuit diagram illustrating one embodiment ofthe invention;

FIG. 2 is a simplified circuit diagram illustrating another embodimentof the invention.

Firstly, it should be noted that the same parts operating in anequivalent manner are denoted by the same reference numerals in bothfigures.

FIGS. 1 and 2 illustrate an electronic circuit for a charger 1,comprising a charger device 2 for an accumulator 3. The charger 2 issymbolically illustrated by a simple block, and the circuit design maybe any system known from the prior art. For example, the charger 1 mightbe used as an inverter source or the like.

The charger device 2 for accumulator 3 is connected to a power source 6,in particular a mains network, by input terminals 4, 5. The charger 1converts the input energy from an AC voltage into a DC voltage anddelivers this converted power, i.e. the DC voltage, by output terminals7, 8 to a consumer 9, so that the consumer 9, in particular an ohmicconsumer 9, can be supplied with power, and accumulator 3 can becharged.

It should also be pointed out that by means of the protection circuit,which is outlined by dot-dashed lines, the charger 1 is able to runseveral functions, in particular polarity reversal protection, overloadprotection and/or load detection. The individual functions will bedescribed in more detail below. In the illustrated embodiments, theelectronic circuit is designed for a specific potential, in particularthe negative potential, although it would also be possible to operate onthe basis of a different potential, in particular a positive potential.

As illustrated in FIG. 1, a switching element 10 is provided between theoutput terminal 8 for the negative potential of the charger device 2 forthe consumer 9, and if a negative polarity is applied to output terminal8, the switching element 10 is switched on and if the opposite(incorrect) polarity, in other words positive polarity, appears, it isswitched off, the switching function of the control device 11 of thecharger device 2 being operated automatically, as will be describedbelow. The output terminals 7, 8 are disconnected from the inputterminals 4, 5 of the power supply source 6, by means of the chargerdevice 2, so that the individual possible functions, in particularpolarity reversal protection, overload protection and/or load detection,operate on the output side.

Connected to the output terminal 8 for the preferably negative potentialis a drain node 12 of the switching element 10, in particular a MOSfield-effect transistor. Another node 13 of the switching element 10 isconnected to the negative potential. The through connection of theswitching element 10 is therefore connected between the output terminal8 and the negative potential, of the power supply device 1 and if aspecific polarity appears at the output terminal 8, the throughconnection is switched on whereas if the opposite (incorrect) polarityappears at the output terminal 8, the through connection is switchedoff.

A control node 14, in particular a gate node, of the switching element10 is connected to a voltage, in particular a positive supply voltage16, preferably by a resistor 15, as schematically illustrated. Thisconnection may be set up so that the control node 14 is connected to theoutput terminal 7, or a voltage of an independent power source. The keyfactor is that the control node 14 is powered or supplied by a permanentvoltage which is not interrupted by a switch element, i.e. the controlnode 14 of the switching element 10 is continuously supplied withvoltage, preferably a positive voltage. As a result, when this voltageis applied to the control node 14, the switching element 10 isautomatically activated, i.e. when this voltage, in particular thesupply voltage 16, is applied, the switching element 10 is activatedwithout a consumer 9 having to be connected to the output terminals 7,8.

The control node or gate 14 of the switching element 10 is connected toa node 17, in particular a collector node, of another switching element18, in particular a transistor. Another node 19, in particular anemitter node, of the other switching element 18 is connected to thenegative potential. The through connection, in particular thecollector-emitter connection, of the other switching element 18 istherefore disposed between the control node 14 of the first switchingelement 10, and the preferably negative potential.

The drain node 12 of the first switching element 10 is connected to theoutput terminal 8 and preferably by a resistor 20 to a control node 21of the other switching element 18 so that a corresponding voltage can beapplied in order to activate the other switching element 18 connected tothe output terminal 8 by the control node 21 of the other switchingelement 18. The control node 21 is also connected to output terminal 24of the control device 11 of the charger device 2, which is schematicallyindicated by a block and preferably is a microprocessor. The controlnode 14 of the first switching element 10 and node 17 of the secondswitching element 18 are also connected to input terminal 22 of thecontrol device 11.

The essential feature of the electronic circuit proposed by theinvention is that the first switching element 10 can also be activatedwhen the power supply device 1 is switched on, even if no consumer 9,such as accumulator 3, is connected. This is possible because thecontrol node 14 of the first switching element 10 is permanentlysupplied with voltage so that, once this voltage has built up, it isautomatically able to activate the first switching element 10.

As a result of this build-up, the switching element 10 is activated witha specific polarity at the output terminals 7, 8 when the consumer 9 isconnected, even if no power supply source 6 is connected to the inputterminals 4, 5 or the voltage applied to the gate node is activated whenthe control node 14 of the first switching element 10 is connected tothe output voltage, in particular the other output terminal 7, insteadof the supply voltage 16 because this causes a corresponding accumulatorvoltage to appear at the control node 14 of the first switching element10. Consequently, the polarity reversal protection is active evenwithout power supply source 6 connected to the input terminals 4, 5,thereby preventing damage to the components if the accumulator 3 isincorrectly connected to the output terminals 7, 8 when the charger 1 isnot in operation.

The operation of the charger device combined with the protection circuitwill be described in more detail below. As explained above, the chargerdevice 2 is connected by input terminals 4, 5 to the power supply source6, and the supplied power is converted from an AC voltage to a DCvoltage. This converted power is delivered by output terminals 7, 8,which are separated from the input terminals 4, 5 by components such asdiodes or a transformer, etc., to the consumer 9, i.e. the accumulator3. When the charger device 2 is connected to the power supply source 6,the switching element 10 between the output terminal 8 and the negativepotential of a voltage, in particular the supply voltage 16 or an outputvoltage of the charger device 2 or an independent voltage is activated,establishing an electrical connection between output terminal 8 and thenegative potential. As a result of establishing a connection between theoutput terminal 8 and the negative potential, the polarity reversalprotection, the overload protection and/or the load detection becomeoperative because a current circuit can be established by the chargerdevice 2 across the two output terminals 7, 8.

The polarity reversal protection is operated in such a way that, if anexternal voltage source is applied to the output terminals 7, 8 with anegative polarity at the output terminal 8 connected to the accumulator3, the switching element 10 remains switched on whereas if theaccumulator 3 is connected to the output terminal with the opposite,i.e. positive polarity, the switching element 10 is switched off ordeactivated. The way in which this operates is that, if the outputterminals 7 and 8 are at the opposite (incorrect) polarity, the otherswitching element 18 is activated so that the supply voltage 16appearing at or delivered to the control node 14 of the first switchingelement 10 is applied to the negative potential and the first switchingelement 10 is therefore deactivated, i.e. because the polarity at theoutput terminal 8 is opposite (incorrect), in this case positive, thevoltage applied by the connecting line between the output terminal 8 andthe control node 21 of the second switching element 18 is forwarded tothe latter so that the other switching element 18 is activated and thefirst switching element 10 is deactivated by the connection establishedbetween the control node 14 and the negative potential. The firstswitching element 10 remains deactivated until the opposite (incorrect)polarity of the voltage of the accumulator 3 at the output terminals 7,8 is interrupted so that the supply voltage at the control node 21 ofthe other switching element 18 is also interrupted, thereby deactivatingthe other switching element 18 again and the supply voltage 16 at thecontrol node 14 of the first switching element 10 can be built up again,enabling the first switching element 10 to be automatically activated.

It should be pointed out that not just accumulators 3 can be connectedto the output terminals 7, 8. Naturally, it would also be possible toconnect an ohmic resistance or other circuit components which need to besupplied with power from the charger device 2. However, if noaccumulator 3 is connected, it will not be possible to operate polarityreversal protection and the electronic circuit will then only be able torun the overload protection and/or load detection functions.

The overload protection prevents too high a flow of current across thefirst switching element 10, which could damage the switching element 10.In the case of an accumulator 3, too high a flow of current might occurif the latter were totally or almost totally discharged.

In the case of the overload protection, in other words when connectingan empty or almost empty accumulator 3 or another consumer 9 with a highcurrent uptake to the output terminals 7, 8, the first switching element10 is deactivated by the second switching element 18, even if theconsumer 9 or the accumulator 3 is at a specific (correct) polarity. Theway this is operated is that, as a result of too high a current flow, acorresponding voltage appears via the resistor 20 at the control node 21of the other switching element 18 so that, when a specific level isexceeded, the other switching element 18 is activated, therebydeactivating the first switching element 10 in the manner describedabove with respect to the polarity reversal protection. The permissiblecurrent flow across the first switching element 10 can be defined on thebasis of the rating of the resistor 20 in the connecting line to thecontrol node 21 of the second switching element 18 and the rating of theswitching element 10.

When the overload protection is in operation when an accumulator 3 isbeing used as the consumer 9, the first switching element 10 isperiodically switched on and off until the current flow beingestablished across the first switching element 10 falls below a definedvalue and the voltage appearing at the control node 21 of the otherswitching element 18 also falls below a pre-defined value, preventingthe other switching element 18 from being activated. The switchingelement 10 is periodically switched on and off because whenever thefirst switching element 10 is activated, the empty or almost emptyaccumulator 3 connected to it is charged for a brief period, therebyreducing the current level over time and enabling permanent charging.

In order to enable this periodic switching on and off, however, thecontrol device 11 must intervene accordingly, i.e. the second switchingelement 18 must be purposely deactivated by the control device 11 sothat the first switching element 10 is activated again. To do this,however, it is necessary for the control device 11 to detect theswitched state of the first and second switching elements 10 and 18.This is achieved by coupling a control input 22 of the switching device11 with the control node 14 of the first switching element 10 and withthe collector node of the second switching element 18 via a resistor 23,so that when the second switching element 18 is activated, the supplyvoltage 16 appearing at the control node 14 of the first switchingelement 10 is applied to the negative potential, thereby enabling a highor low signal to be generated at the control input 22 of the controldevice 11. As a result, the control device 11 will be able to detect thestate of the switching elements 10 and 18 for all functions, in otherwords for the polarity reversal protection and/or load detection. Withan electronic circuit design of this type, the two switched states ofthe switching elements 10 and 18 can be detected on the basis of onlyone signal, i.e. a high or low signal, since the two switching elements10 and 18 are always in a complementary switched state, i.e. when thesecond switching element 18 is activated, the first switching element 10is deactivated and vice versa.

To enable the control device 11 to activate the second switching element18, the control device 11 has a control output 24 connected to thecontrol node 21 of the second switching element 18, preferably via aresistor 25. By means of this connection, the control device 11 cancontrol the second switching element 18 by applying a signal to thecontrol node 21. This can be operated in such a way, for example, thatwhen the first switching element 10 is deactivated by the control device11 on expiry of a pre-set period, the second activated switching element18 is deactivated by transmitting a negative signal, so that the voltageapplied to the control node 14 of the first switching element 10activates the first switching element 10 again. This switching sequencecan be repeated by the control device 11 any number of times to enablethe first switching element 10 to be periodically switched on and off.Naturally, the system could be set up so that, after a pre-definednumber of switching sequences, the control device 11 does not initiate afurther switching sequence and an error signal is put out.

In order to be able to operate a load detection system, the controldevice 11 automatically controls the switching elements 10 and 18. Forload detection purposes, the control device 11 firstly deactivates thefirst switching element 10 by activating the second switching element 18and, on expiry of a pre-set period, activation of the second switchingelement 18 is terminated so that, if a consumer 9 is connected, avoltage will appear at the control node 21 of the second switchingelement 18, in which case the first switching element 10 will remaindeactivated, due to the voltage appearing at the control node 21. Thisis detected by the control device 11 at the control input 22 andindicates that a consumer 9 is connected. By adopting this approach, itis possible to connect an ohmic resistor or other circuits groups ordevices as consumers 9.

To enable the control device 11 to detect an accumulator 3 at the outputterminals 7, 8, another control procedure is necessary in addition tothat described above. This is necessary because, when an accumulator 3is connected at the same voltage level as the output voltage. of thecharger device 2, no voltage is registered across the resistor 20 at thecontrol node 21 of the other switching element 18 and it is not possibleto operate a self-holding function.

To operate a load detection of an accumulator 3, whilst the firstswitching element 10 is deactivated, the control device 11 raises theoutput voltage at the output terminals 7, 8 from the charger device 2 bya certain amount, in particular between 1V and 5V, causing the controldevice 11 to terminate activation of the second switching element 18, asa result of which, when an accumulator 3 is connected, voltage isapplied to the control node 21 of the second switching element 18because of the voltage difference between the accumulator voltage andthe output voltage of the charger device 2, and the second switchingelement 18 will therefore remain active because of the self-holdingfunction, as described above, and this will in turn be detected by thecontrol device 11 at the control input 22.

It should be pointed out that the polarity reversal protection can beoperated independently of any intervention from the control device 11,whereas in the case of the overload protection and/or load detection,the control device 11 must be used, so that these functions are run orrepeated after the charger device 2 has been switched.

FIG. 2 illustrates another embodiment operating on the same principlesand control sequences as those described with reference to FIG. 1.

The difference is that the control node 14 of the first switchingelement 10 is directly connected to a control output 26 of the controldevice 11, so that the connecting line illustrated in FIG. 1 to theother switching element 18 and hence to the supply voltage 16 or to theoutput voltage of the charger device 2 is interrupted.

To enable the polarity reversal protection, the overload protectionand/or the load detection system, to be run by the charger device 2, theswitching element 10 will have to be controlled from the control device11, i.e. in accordance with the operating sequence described with regardto FIG. 1, the control device deactivates the switching element 10 whenthe switching element 18 is activated and vice versa. Such a controlsystem can be operated by the control device 11 because the controldevice 11 is able to detect the switched state of the second switchingelement 18 at the control input 22 and the first switching element 10can be controlled accordingly by the control device 11.

What is claimed is:
 1. A charger for an accumulator, comprising a powersource, a charging device connected by input terminals to the powersource and by output terminals to the accumulator, the power supplied bythe power source being converted from an AC voltage to a DC voltage andthe converted power being delivered by the output terminals to theaccumulator, and an output side protection circuit for overloadprotection and polarity reversal protection against incorrect polarityof the accumulator, the protection circuit being connected to one of theoutput terminals and including a first switching element connected tothe one output terminal and a negative potential of the charging deviceand establishing a connection between the one output terminal and thenegative potential if a correct, negative polarity appears at the oneoutput terminal, and interrupting the connection if an incorrect,positive polarity appears at the one output terminal, a control node ofthe first switching element connected by a conductor to a secondswitching element to which the negative potential of the charging deviceis connected; and the charging device further including a control devicehaving a control input terminal and a control output terminal, thecontrol input terminal being connected with a positive potential of asupply voltage source so that the second switching element is activatedif an incorrect positive polarity appears at the one output terminal ortoo high a current flows through a conductor between the one outputterminal and a control node of the second switching element, causing thefirst switching element to be deactivated, due to the connectionestablished by the second switching element between the supply voltagesource and the negative potential of the charging device, the switchedstate of the first switching element being determined by the switchedstate of the second switching element, and the control output terminalbeing connected to the control node of the second switching element forcontrolling the further switching element.
 2. The charger device ofclaim 1, wherein the supply voltage source is the positive potential ofthe charging device.
 3. The charger device of claim 1, wherein thesupply voltage source is the output voltage of the charging device atthe other one of the output terminals.
 4. The charger device of claim 1,wherein the supply voltage source is independent of the charging device.5. The charger device of claim 1, further comprising a drain node of thefirst switching element connected to the one output terminal and to thecontrol node of the further switching element.
 6. The charger device ofclaim 1, wherein the control node of the first switching element and theconductor of the second switching element are connected to the controldevice of the charger device.
 7. The charger device of claim 1, whereinthe control node of the first switching element is connected to thesupply voltage source and receives voltage therefrom.
 8. The chargerdevice of claim 1, wherein the control node of the first switchingelement is connected to another one of the output terminals, receivingthe output voltage of the other output terminal, causing the firstswitching element to be activated when the accumulator is connected tothe correct polarity across the output terminals even if the powersource is disconnected from the input terminals.
 9. A method ofcontrolling a charger for an accumulator connected to input terminals toa power source to supply power to the charging device, comprising thesteps of converting the supplied power from an AC voltage to a DCvoltage, and supplying the converted power to output terminals connectedto the accumulator; connecting an output side protection circuit foroverload protection and polarity reversal protection to one of theoutput terminals, operating a first switching element in the protectioncircuit to maintain a connection between the one output terminal and anegative potential of the charging device if a correct, negativepolarity appears at the one output terminal, and to interrupt theconnection if an incorrect, positive polarity appears at the one outputterminal, activating the first switching element when the chargingdevice is connected to the input terminals of the power supply sourceeven when the accumulator is not connected to the output terminalswhereby the incorrect polarity protection is activated, and activating asecond switching element in the protection circuit if an incorrectpositive polarity appears at the one output terminal or too high acurrent flows through a conductor between the one output terminal and acontrol node of the second switching element, and causing a supplyvoltage applied to a control node of the first switching element to beapplied to the negative potential and to deactivate the first switchingelement.
 10. The method of claim 9, comprising the step of activatingthe first switching element by the second switching element for overloadprotection when the correct polarity appears at the output terminals andtoo high a current flows through the first switching element.
 11. Themethod of claim 9, comprising the step, for overload protection, ofperiodically switching the first switching element on and off until thecurrent flow through the first switching element and the voltage at thecontrol node of the second switching element fall below a defined value,whereby the further switching element is prevented from being activated.12. The method of claim 9, comprising the steps of deactivating thesecond switching element and automatically reactivating the firstswitching element after the first switching element has been deactivatedon expiry of a pre-set time by a control device of the charger device.13. The method of claim 12, comprising the steps of first deactivatingthe first switching element by the control device by activating thesecond switching element and, on the expiry of a pre-set time,deactivating the second switching element, applying a voltage to thecontrol node of the second switching element if the accumulator isconnected, causing the first switching element to remain deactivated,and detecting the deactivation of the first switching element by thecontrol device.
 14. The method of claim 12, comprising the steps ofincreasing the output voltage at the output terminals by the chargerdevice by a defined amount, deactivating the second switching element bythe control device so that, if the accumulator is connected, a voltageappears at the control node of the second switching element, anddetecting the activation of the second switching element by the controldevice.
 15. The method of claim 12, comprising the step of detecting thedeactivation of the first switching element and an activation of thesecond switching element by the control input terminal of the controldevice, and applying the voltage at the control node of the firstswitching element to the negative potential.